Return to Tonga at The Crossroads, after investigating the Stagnant Oasis.
Like the one you found at the Forgotten Pools, there may be fissures at the other oases in the Barrens. If so, then perhaps the fissures are the oases' source of life.
We must test this.
Here, take these seeds. They are dead and infertile, but take them to the Stagnant Oasis to the southeast. If there is a fissure there, then place the seeds within it...and observe.